Since I'm currently only level 16, what I do after this depends on how things are going as I advance.
At level 8 I took Maneuvers since it adds to my defense as well, maybe giving me a little better chance of escaping when my bots fall (I don't attack directly so adding +damage to me is useless). I've tried Assault but it uses a lot more endurance and you can't put damage enhancements in it.
At level 10 I took Recall Friend to get my bots unstuck (I've had them knocked into a wall, I hate dismissing/resummoning them, and it works great getting team members together). I haven't used Teleport Foe and most teams are too impatiant to use the finess of it.
Here are my thoughts as they currently stand on what I'll take as I advance:<ul type="square">[*]1. At 18 I want to get Shadowfall to give me increased defense and some stealth. I may take Repair instead depending on how well my Twilight Grasp is working.[*]2. Howling Twilight is a nice power as it auto-hits and has a short disorient (breaking concentration on any active powers even in PvP). And being able to raise fallen team members will be a good thing.[*]3. I want to get Assault Bot as soon as possible (level 24) and I'll need to get Repair before this so I can quickly heal the Assault Bot since it's going to take a LOT of agro (thus setting Repair at level 22).[*]4. I want to get Upgrade Robot as soon as possible so that's at level 32.[*]5. I want to get Dark Servant as soon as possible and that's at level 38.[/list]This leaves me with 4 extra powers I can pick up (the ?? Power in my list at levels 22, 28, 30, and 35). Here are my current thoughts on this (subject to change without notice): 
<ul type="square">[*]I will have all the Robotics powers I want.[*]There are 3 more Dark Miasma powers that look interesting (Fearsome Stare at 20, Petrifying Gaze at 28, and Black Hole at 35). Petrifying Gaze and Black Hole both are a single target only, and Petrifying Gaze is only about 50% effective.[*]I'm having some endurance problems currently from the toggles so I'd like to get Stamina. However, I'll have to eat two more slots getting Swift (or Hurdle, probably Swift) and Health first.[*]I'd like to get Hover so I get the added defense and it helps when teleporting across a zone. It also keeps you off the ground when someone uses an AoE affecting everyone on the ground (like Earthquake).[*]Team Teleport looks interesting however I probably won't get it.[/list]
It might be interesting to see what enchants you have in your slots. I wouldn't say Bots are better than Mercs based on the ability of the group as a whole to heal itself. Repair is a love/hate thing with me. Yes it heals a ton, but the recharge is also really long. You already have a heal via the Dark power set. If you added heal/aid other via the medic pool set instead of repair, you would likely be much better off. I can't remember how many DOs I got in repair right now, but the rechange time is an issue with me currently. Maybe I'll get three SOs in there and play test it before a future respec makes me switch to being able to heal others. Also note repair works only on your pets and not teammates. Having that second heal for people who don't get healed by your dark heal will be thankful for the back up. As a person who plays a couple Emp defenders, that second heal can be huge sometimes.
About end issues, maybe you are more active than I am, but after all my pets are unpacked and buffed, I have a hard time thinking of when end was really an in battle issue.
One thing to note that the damage increase from assault is higher than the defensive increase from manuvers. Yes, I took manuvers too, but I may respec out of it and go assault.
I can't recall how many power pools you have used, or are planning on using, but with four powers to burn, think about grant invis. Fairly cheap pet/teammate defensive boost. You have some stealth, so you won't stick out like a sore thumb after you stealth your bots.
As a person who uses Traps, I'm thinking of respecing out of beacon and just going Medicine pool there. Even in a boosted state, the number of times I would rather have beacon versus a medicine power power is almost nil.
One note about MMs in general, SJ takes the least amount of end to use in terms of a travel power. This can be a really nice thing to use when setting up everything the first time inside of mishes because it takes a large amount of your end. CJ also gives you some added defense which is nice. I could easily add why the other two main travel powers are worth taking too, but I'm just saying why I took SJ as mine. Also note some buildings are JUST tall enough that you can't SJ past them until maybe at a much higher level.
- lvl21 Bot/Trap MM
Actually, this list is how I wished I had set up my character. I actually took Maneuvers at 8, Assault at 10, Tactics at 14 and Recall Friend at 16. So my current travel power is the holiday jet pack and I'm wishing I had gotten RF earlier so I could have teleport now. By using Maneuvers, Assault, and Tactics on all the time my endurance goes up real slow. By using TG I go down slowly in endurance. Throw in Darkest Night (toggle) on a boss and then I start having problems.
Now my current dilema is either start all over or wait until level 24 and burn my first respec in fixing my problem (I don't know if you can do the same respec mission twice). Either way it sucks. 
I wish that the holiday mission included a free respec like I heard they did last year.
P.S. I'm using all training enhancemets currently. I'm going to wait until 17 to get DOs. If you start buying DOs at 12 (the lowest level DOs are 15 so you can start slotting them at 12) then you quickly run out of infamy. I'd rather have everything slotted with training enhancements than only a few with DOs. When I reach 17, I should have enough infamy saved to instantly slot everything with level 20 DOs. I'll probably do the same with SOs (wait until 27 instead of 22) for the same reason.
Uhm yeah Force Feilds is a good power set just slap em on any minions and they will have a better preformance
that and the Medic can heal thats why i gave 2 heal for my SOilders
I'm trying the force field set now. Currently level 6. So far, it's a lot easier with Dark Miasma (as long as I put at least 3 accuracy in Twilight Grasp so I rairly miss) so I can stand by my bots and heal them. I wonder if you can use Aid Other (Medicine Power Pool) on your pets. If so, then that may be an alternative. I'll have to wait till level 8 to see if it works.
Ok a few thoughts here. I have a Merc/Traps MM whose's now in the mid 30's. (and a Zombie Dark in the 20's) While I do have a few issues with the current build I've not felt the need to respec it yet.
One thine I like about mercs over robots is that the Medic heals me as well as healing the other pets. He doesn't however heal himself so you need a way to keep him alive and medicine does that nicely.
Of the Mercs Pool I've taken everything bar the M30 Grenade, I felt that doing AOE's was just a way of attracting agro on me rather that having my pets take the damage. I may change this if I respec.
The one Power I've taken from the line that I just don't use is Serum. It doesn't seem to turn my Commando into a mega killing machine when I use it so it will probably go when I respec.
From Traps I've gone with Caltrops, Acid Mortar, Force Field and Drones. Not sure If I'll take the various traps or Detonate - seems foolish to kill your main attacking ability by bumping off your own minions - may take this before respecing just for kicks and Giggles. Traps could be useful if I use the Spec Ops sniper ability to pull mobs on to them, but I'm running out of slots for powers so not certain as yet. Plus groups don't usually want to wait while Traps get laid before pulling.
For the Pools
My initial power at lvl 6 was Medicine and I've never regretted taking it. Aid other, which does work on your minions, is much more useful than Beacon. which I've not taken, having spoken with a number of other MM's who did, and having seen it being used I think aid other is far better, although when you're getting continually interupted by AOE attacks it can be a pain. I've seldom missed having beacon. Probably won't take Aid Self as being interuptable its usually useless when you need healing most.
I now have all three basic leadershp powers and won't get vengeance. Running all three toggles is an endurance hog but slotting with End reducers deals with this. My intention with these was to slot two end reducers and then 1-2 in appropriate buffs, (though I'm currently running with 3 end reducers in Assault, which I'll probaly stick with) This seems to work reasonably well - though end was a problem until I managed to get the end reducers in.
I've taken stamina on just about every alt I've created except for my MM's. OK at the start of missions all the summoning/buffing is a real end drain and I usually have to kick a rest in, but that just allows the tactical mastery to recycle so its not too bad. During missions themselves I'm usually fine unless I get all excited and start blasting away, rather than controlling the pets.
My final pool power is Speed. I may respec out of this. I partially took this pool for hasten as having powers up faster gives me more options, and partially for SS itself. I don't find it a problem with leaving minions behind as I don't usually run it on missions and don't usually travel with minions in tow.
I spend most of my time on missions directing the minions so I'm not so certain Hasten is needed. It could be replaced by dropping a few recharge enhancers into one or two powers.
I've played a little bit with several Masterminds. Masterminds make the best solo players (since your pets can keep most of the agro leaving you alone) and pretty good team players, however they suck in PvP since the other players will ignore your pets to take you out and when you fall so do your pets. So far I've tried all four primary powers and three of the secondary powers. The combination I like the best is Robotics/Dark Miasma (I have one at level 16). Here's my thoughts on each type;
Primary Powers:
Undead (Necromancy) & Ninjas - prefer close range combat so they're more likely to run up to an enemy for combat. Personally, I like to stay close to my minions to heal them and I'd prefer to stay at a longer range.
Mercenaries & Robots - prefer long range combat so they're more likely to stand in place and shoot rather than run to the enemy (although they will occasionally do so). With Robots, you get can your first Protector at level 12 (which can heal other robots) and the second at level 24 and at level 18 you can pick up the "Repair" power to heal one robot to full health. With Mercenaries you only get one medic at level 18 (the third of your "Soldiers" - I don't know if the Medic can heal you or other members of your team) and no other power to heal your mercenaries. So all in all, I believe Robotics is the better choice here.
Secondary Powers:
Forcefield & Trick Arrow - I haven't tried these, but just from the descriptions I'm not sure if they fit my style of play.
Traps - You have to wait until level 4 to pick up the Triage Becon to heal yourself/others. It doesn't heal very fast and has a long recharge time. Also, this set doesn't buff/debuff very well and you have no way to raise fallen team mates.
Poisons - You get an ok heal at level 1 (Alkaloid) to heal someone on your team or one of your pets (including robots) but not yourself. It's a bit of an endurance drain and doesn't heal as well as the DM power Twilight Grasp, however, it works every time and you can use it at range. At level 16 you can get "Elixir of Life" to raise fallen team mates. There are also several nice debuff skills in this set.
Dark Miasma - You get a good heal at level 1 (Twilight Grasp) for yourself and others near you (including your pets) and this also debuffs your target, however, you have to hit an enemy and you have to be close to those you want to heal (which can be dangerous with AoE enemies). At level 10 you can get a power to raise fallen team mates (Howling Twilight) however you need to be close to them and have an enemy nearby so having Teleport Foe will be a nice power pool to have with this power. At level 38 you can summon yet another pet (Dark Servant), I haven't gotten this yet but may be a nice pet to have. There are also several nice debuffs in this set.
Power Pools for the Mastermind:
Leadership - great as long as you stay near your pets to increase their defence, damage, and accuracy. Vengance will not work if one of your pets fall, so it may not be a good power to have if you solo a lot.
Fitness - Stamina at level 20 is a great power to have. Health at level 14 is also very nice.
Teleport - Teleport Friend is a good power to get stuck pets to you and nice when teaming (including getting a fallen team mate out from under some enemies). If a pet gets stuck in a wall and you don't have this the only to fix this is to dismiss and then resummon/upgrade it. Teleport Foe is a nice power to have however, it takes some finess and a lot of practice to use it properly. Teleport is the fastest means of travel.
Flight - Hover is real nice when teleporting around and adds to your defense however you move real slow. Air Superiority is nice to knock those flyers out of the air. Fly is pretty good movement power, however you can't take your pets and you lose a lot of accuracy. Group Fly doesn't work well with pets since they'll move slower than you.
Pet notes: The more pets you can summon of the same type, the lower in level from you they are. If you can only summon one, then it is at your level. If you can summon 2, then they are at one level below you, and if you summon 3 then they are at two levels below you. If you level (like in the middle of a mission), any pets you have already summoned will remain at their old level until you resummon them. Once you have both upgrades to your pets, you have to use both of them on all your pets to get them fully upgraded (the level 32 upgrade doesn't include the level 6 upgrade). Thus at level 32 you can summon 6 pets with 3 powers and you will have to use both upgrade powers on each pet giving you a total of 12 times you have to use your upgrades on your pets.
Mastermind Problems:
Whenever you change zones all your pets go away (including entering/exiting a Mission map although changing maps within a mission doesn't). On some missions, there are enemies waiting to ambush you when you enter and since you have no pets it can be very painful.
With all this in mind I've decided for my character I want to get Teleportion and Leadership fast. Since my highest MM is level 16, there's 4 "?? Power" (meaning I haven't decided what I want to put there yet). Therefore, I've come up with the following training order for a Robotics/Dark Miasma character (it can be adapted to other combinations with very little work);
Level 1: Robotics -> Battle Drones & Dark Miasma -> Twilight Grasp. 3 Inspiration slots.
Level 2: Dark Miasma -> Tar Patch. +1 Inspiration slot (4).
Level 3: +2 Slots (one in Battle Drones & one in Twilight Grasp). +4 Inspiration Slots (8).
Level 4: Dark Miasma -> Darkest Night
Level 5: +2 Slots (both in Battle Drones)
Level 6: Robotics -> Equip Robot (you also get your second Battle Drone now).
Level 7: +2 Slots (Both in Twilight Grasp)
Level 8: Power Pool - Leadership -> Assault (+damage) or Maneuvers (+defense)
Level 9: +2 Slots (Both in your leadership pool)
Level 10: Power Pool - Teleportation -> Recall Friend or Teleport Foe. +2 Inspiration Slots (10)
Level 11: +2 Slots (both in Twilight Grasp - I use this a lot)
Level 12: Robotics -> Protector Bots
Level 13: +2 Slots (one in Protector Bots, one in Darkest night)
Level 14: Power Pool - Teleportation -> Teleport
Level 15: +2 Slots (both in Teleport). You also get your first title.
Level 16: Power Pool - Leadership -> Tactics (+ accuracy)
Level 17: +2 Slots (both in Tactics)
Level 18: Dark Miasma -> Shadowfall (you also get your third Battle Drone)
Level 19: +2 Slots
Level 20: Dark Miasma -> Howling Twilight. You also can get a cape and another costume slot.
Level 21: +2 Slots
Level 22: ?? Power
Level 23: +2 Slots
Level 24: Robotics -> Repair (you also get your second Protector Bot)
Level 25: +2 Slots. +5 Inspiration Slots (15). You also get your second title.
Level 26: Robotics -> Assault Bot
Level 27: +2 Slots
Level 28: ?? Power
Level 29: +2 Slots
Level 30: ?? Power. You also can get aura(s) and another costume slot.
Level 31: +3 Slots
Level 32: Robotics -> Upgrade Robot
Level 33: +3 Slots
Level 34: +3 Slots
Level 35: ?? Power
Level 36: +3 Slots
Level 37: +3 Slots
Level 38: Dark Miasma -> Dark Servant
Level 39: +3 Slots
Level 40: +3 Slots. +5 Inspiration Slots (20). You also can get another costume slot.
I hope this helps you set up your R/DM MM!